Embodiments of the present invention relate to a support ring to support a substrate in a process chamber.
In the processing of substrates, such as semiconducting wafers and displays, the substrate is placed on a support in a process chamber and suitable processing conditions are maintained in the process chamber. For example, the substrate can be heated in a controlled heating cycle to thermally process the substrate. The substrate can be heated, for example, by an array of heating lamps disposed above or below the substrate in the chamber. Thermal processing can be used, for example, to anneal a layer that has been ion-implanted on the substrate, perform thermal oxidation or nitridation processes, or perform thermal chemical vapor deposition processes on the substrate.
However, variations in temperature gradients across the substrate can result in non-uniform processing of the substrate. Non-uniform temperatures occur at different substrate regions because of, for example, non-uniform convection or conduction heat losses from regions of the substrate in contact with the support or other chamber components and substrate regions not in contact with the support. It is particularly difficult to achieve temperature uniformity across the substrate when the substrate is heated at rapid heating rates, such as in rapid thermal processing (RTP) systems. Thus, it is generally desirable to maintain uniform temperatures across the substrate during thermal processing to provide uniform processing results.
The temperature gradients in the substrate have been reduced using a substrate support ring that extends outwardly from the substrate to surround a periphery of the substrate. The ring effectively expands or pushes out the temperature gradients in the substrate from the substrate periphery to the outer edges of the ring. The support can also have a top surface made of a material that has heat absorption properties similar to that of the substrate to further equalize temperatures between the substrate center and periphery. For example, a support ring comprising silicon carbide coated with silicon is described in U.S. Pat. No. 6,280,183 to Mayur et al, and U.S. Pat. No. 6,200,388 to Jennings, both assigned to Applied Materials, and both of which are herein incorporated by reference in their entireties.
However, even such support rings can fail to provide adequate temperature uniformity across the substrate in rapid heating rate processes, for example, processes having heating rates of at least about 200° C./second. In these processes, the difference in heating rates between the support ring and the substrate generates temperature gradients along the periphery of the substrate that become unacceptably high during the heating process step. For example, use of a conventional ring in a rapid heating rate process can cause temperatures across the substrate to vary by at least about 15° C., which is excessively high.
Accordingly, it is desirable to have a support ring that does not generate excessive temperature gradients in a substrate during thermal processing. It is also desirable to have a support ring that heats at a rate that is sufficiently close to the heating rate of the substrate to reduce the formation of temperature gradients in the substrate.